Quasi-linear theory (QLT) introduces corrections to the Havelock integral and makes it possible to operate with realistic wave amplitudes and length into framework of linear theory. These corrections for wave amplitude and length are based on implicit employment of the model 2D problems for nonlinear waves of highest magnitude (Stokes waves). There is both description of algorithms and comparison with towing test results for diverse ships here. A substantially novel (and environmentally important) aspect of this paper is application of QLT to computation of ship wave resistance in shallow waters.

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A large number of recreational craft are now built throughout the world. This has resulted in the possibility of using different outboard motors and types of outboard motor propellers. These propellers have been developed by trial and error over the past decades. Consequently they represent a state of the art for a number of propeller designs including the "cupped propeller" with a bent trailing edge. The present paper presents an overview of these outboard motor propellers. It then examines the possibilities for the performance improvement when the propellers are designed and manufactured with spoilers. Finally the results of systematic calculations are presented to illustrate the possibility of the propeller with spoiler for cavitating outboard motor propellers.